Shrouded shackle locks with curved shackles are old. Locks rekeyable by replacement of the lock cylinders or parts therein when the locks are in their open position have earlier been proposed (U.S. Pat. Nos. 4,290,279; and 4,138,868). Locks in which tools can be inserted only when the lock is unlocked are also known (U.S. Pat. No. 3,977,221).